In a Long Term Evolution (LTE) communications system, channel sounding information is obtained by user equipment (UE) by sounding a downlink transmission channel and quantizing a sounding result and is reported by the user equipment to a base station, so that the base station can obtain an interference status of downlink transmission.
The channel sounding information includes a channel quality indicator (CQI) and a channel sounding reference signal (SRS). UE sounds a downlink transmission channel to obtain a CQI, and feeds back the CQI to a base station on an uplink channel. The base station determines a modulation and coding scheme of the UE based on the fed back CQI. In addition, the base station estimates channel state information of a downlink channel by using an uplink SRS and reciprocity between the uplink channel and the downlink channel, to obtain a channel matrix of a multi-transceiver-unit system. Based on the channel matrix, co-frequency and co-time transmission of a plurality of UEs can be implemented on the base station by using a precoding technology, thereby improving spectrum utilization of the system.
In a current standard, feedback of a CQI and an SRS includes two types: periodic feedback and aperiodic feedback.
For periodic CQI feedback, a CQI is carried by using a physical uplink control channel (PUCCH), and a time interval of the feedback is implemented through semi-static configuration by using higher layer Radio Resource Control (RRC) signaling. For aperiodic CQI feedback, a CQI is carried by using a physical uplink shared channel (PUSCH). The feedback is triggered by receiving downlink control information (DCI). Each time the UE is triggered, the UE feeds back all sounded CQIs at a time by using the PUSCH. Frequency of periodic feedback of an SRS is configured by using higher layer RRC. Aperiodic feedback of an SRS is triggered by receiving DCI. After each trigger, the UE transmits the SRS only once on the last symbol of a configured subframe.
In a future evolved cellular network system, a very high requirement is imposed on channel sounding information obtained by a base station. That is, sounding frequency of the channel sounding information needs to be increased. Therefore, a feedback interval of a CQI or an SRS needs to be shortened. However, dynamically changing feedback frequency by increasing a quantity of times of aperiodic feedback or by using RRC configuration leads to problems that overheads are increased and a configuration response is not timely, and consequently, overall spectrum utilization of the system is affected.